Recent Adv Anc~ in the Chemistry of Condensed Tannins
نویسنده
چکیده
The presence of the procyanidins epicatechin-( 4j3-8)-catechin. epicatechin..{ 4j3-6)-catechin. catechin( 4a-8)-catechin. epicatechin-( 4j3-8 >-epicatechin-( 4j3-8)-epicatechin-{ 4138)-catechin. and epicatechin-(4j3-8)-epicatechin-(4j3-6)catechin in tile phloem of PillU.f raeda demonstrated heterogeneity in the location of the interftavanoid bonds in oligomeric procyanidins. Panial acid-catalyzed cleavage of polymeric procyanidins from Pinus raeda and Pinus palusrris barks or Photinia glabr~scens leaves gave both the epicatechin-(4j3-8)-epicatechinand epicatechin-(4j3-6)epicatechin-benzyl or phenyl sulfides. demonstrating isomerism in tile interflavanoid bond location in these polymers. Comparison of tile rates of acid-catalyzed cleavage of isomeric dimen showed that those compounds with a (4~-6) interftavanoid bond were more stable than compounds with a (4~-8) bond. Also. catechin-(4a-8)-catechin was more resistant to cleavage than either epicatechin(4j3-8)-catechiD or epicatechin-(4j3-8)-epicatechin when heated in the presence of excess phenylmethanethiol with acetic acid. The structures of condensed tannins and the stability of these polyrnen under acidic conditions ate discussed. .
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